ABS systems have developed from the original high cost, bulky devices to the point where ABS systems are now standard on many vehicles. One of the principle components of an ABS system is a high pressure pump which enables rapid pulsing of the brake components when the system detects a lock condition. Such pumps may also be used in vehicle control systems. Hereinafter, pumps or systems for both ABS and TCS will be referred to as "ABS pumps or systems." High pressure pumps may be made of cast iron or steel with a steel piston driven by a kinematic chain, generally a cam-type eccentric or serpentine-type oscillatory drive member. The piston is forced against the drive member by the pressure of a spring incorporated within the cylinder in which the piston travels.
In order to seal the fluid within the pump, a high pressure O-ring type seal has been located in a circumferential groove in the piston element. Pumps such as these have been highly effective and demonstrate minimal wear on the pump body due to abrasion at the seal/pump body interface.
The weight of such pumps is considerable, however, and efforts have been made to reduce the weight of the pump. To this end, a sleeve-type pump has been developed which employs aluminum as the pump body and a steel or cast iron sleeve within which the piston travels. In sleeve-type pumps, however, the aluminum body must be made larger than desirable in order to accommodate the sleeve without weakening the body. Moreover, it is necessary that the sleeve itself be sealed with respect to the body, and thus multiple O-ring seals must be used.
The need to incorporate a separate sleeve with its attendant seals decreases, to an extent, the advantages of reducing weight through the use of an aluminum pump body. The necessity of providing and machining a separate sleeve further adds to manufacturing costs. Furthermore, the traditional location of inlet and outlet check valves, necessary to achieve one-way flow of fluid, adds complexity and attendant cost to the machining and assembly of high pressure ABS pumps.